For analysis of biological samples, it is often desirable to use only a small sample volume. Therefore, a precise measurement of the volume could be crucial to the analysis accuracy. In the applications of point-of-care testing (POCT), the analysis of biological samples is preferably conducted in a disposable cartridge, which has the merits of ease of use and avoids cross-contamination from other samples. However, sensing volume in cartridges imposes new challenges particularly to measure a small volume with high accuracy. For example, the complexity of the cartridge limits the available choices of volume sensing methods.
Normally these cartridges use passive methods such as volumetric chambers to determine the fluid volume taken for analysis. The accuracy of these passive methods suffers from unpredicted variations, such as user operations (e.g. the volumetric chamber is not filled up properly or contains bubbles). These variations are particularly ubiquitous in POCT applications, where users replace cartridges before each analysis.